For the integrated services digital network--ISDN--it is estimated that about 2 million potential users are interested in a low-bit-rate ISDN packet service (D channel). The ETSI (European Telecommunications Standards Institute) is currently drawing up standards which define the various types of accesses to X.25 packet services by ISDN subscribers. Packet switching is to be implemented in the D channel ("ISDN-Paketdienste", Elektrisches Nachrichtenwesen, Vol. 64, No. 1, 1990, pp. 41 to 50 "ISDN: European and Worldwide Standardisation", Electrical Communication, Vol. 64, No. 1, 1990, pp. 51-56.
To permit the connection of data terminals with X.25 interfaces to a digital exchange in the ISDN, use is made of CCITT (International Telegraph and Telephone Consultative Committee) X.31 Recommendation.
To switch packet data in the D channel through a digital exchange, a so-called frame handler or a so-called frame switch is commonly inserted in a connection to control communication between two data terminals, OSI (Open System Interconnection) Layer 2 and OSI Layer 3 functions. Such a frame switch consists of a processor and a switching unit and controls the connection setup and the handling of the packet data. As a result, the processor required for the OSI layer 3 functions is very heavily loaded by the D channel packet handling.